Hoist control system



July 27, 1943. H. L. WILCOX 2,325,454

HOIST CONTROL SYSTEM Filed Au l25, 1941 2 Sheets-Sheet 1 soo-- g 200-aoo J .J .J 3 LL -|oo s'o o so 100 INVENTOR PER CENT SYNCHRONOUS SPEEDHARRY wn 0x POWER HOISTING & LOWERING KEY --smcsu: PHASE BRAKING BY 5 ia "COUNTER TORQUE LOWERING WW2: $42M) J 1943- H. L. wlLco x 2,325,454

HOIST CONTROL SYSTEM Filed Aug. 25, 1941 2 Sheets-Sheet 2 1NVENTOR HARRYL. WILCOX Patented July 27, 1943 v UNITED STATES PATENT OFFICE I I2,325,454 I HOIST CONTROL SYSTEM Harry L. Wilcox, Cleveland, hio,assignor to The Electric Controller & Manufacturing Company, ICleveland, Ohio, a corporation of Ohio I Application August 25, 1941,Serial No. i08,153

16 Claims.

This invention relates to electric systems of control for alternatingcurrent induction motors which are utilized as the driving motors forapparatus in which the load at times overhauls the motor and drives it,and in which the overhauling load must be retarded to prevent theoverhauling speed from becoming excessive and, at times, must be broughtto a full stop. The invention is particularly applicable to hoist motorswhich may be overhauled and driven by a descending load, andtheinvention is hereinafter described as applied to that use.

Heretofore when polyphase wound rotor induction motors have been used tooperate electric hoists, descending loads have been retarded by shortclrcuiting a portion of the primary winding of the motor andconcurrently energizing a portion of the primary winding with singlephase current while maintaining a. predetermined amount of resistance inthe secondary circuit of the motor. The single phase braking actionresults from the rotation of a rotor circuit of high resistance throughan unsymmetrical field set up due to energization of the primary from asource of power having preponderantly single phase characteristics andthe presence of a. local closed path of low resistance in the primarycircuit. As used herein, single phase source of power refers to a sourcehaving preponderantly single phase power dharacteristics and singlephase braking refers to braking action obtained by connecting theprimary to such a source with a portion of the primary short circuited,i. e., connected in a local circuit of low impedance. This type ofcontrol has proved very successful for a large proportion of electrichoist applications, and is particularly well suited for hoists requiringaccurate inching control.

Also, in hoists equipped with Dolyphase wound rotor induction motors,counter-torque control has been used in which descending loads areretarded by connecting the motor to a source of power havingpreponderantly poiyphase characteristics for causing the motor to exerta motor torque which is opposed to the torque of the descending load.Since the opposition or reverse motor torque must also be used to hoistthe load, and since for hoisting operations the reverse torque must bevaried throughout a range of high values, whereas for optimum resultsduring lowering operations the reverse torque should be variablethroughout a range of smaller values, difficulty has been experienced inproviding a simple control system which is readily adjustable to givetwo such ranges of reverse torque.

Furthermore, counter-torque control systems lack accuracy in the controlof small and inching movements of the load. A further complication isinvolved when it is desired to include in such control systems a meansto control accurately small movements 01 the load and to bring the motorto a complete stop while constraining the motor from reversing the load.

In accordance with this invention a control system for a polyphase woundrotor hoist motor is provided in which the operator of the hoist mayselect at will one of the two ranges of reverse torque. For hoistingoperations, movement of the master switch through successive hoistingpositions results in short circuiting of the secondary resistance insteps to give several values of reverse torque from a moderately lowvalue to the maximum torque of the motor. The secondary resistance is soconstituted that, upon operation of an auxiliary switch, the hoistingpositions 01 the master switch are rendered eii'ective for shortcircuiting of the secondary resistance in steps in such a manner that attimes the secondary circuit is unbalanced and a group of torque valuesvarying throughout a predetermined low range suitable for loweringoperations or countertorque braking is obtained.

Counter-torque control of the improved type disclosed by this inventionis most suitable when. loads must be lowered long distances at slowspeeds. Such conditions are commonly encountered in the operation 01'shipway cranes. On the other hand, for short movements and inchingoperations, all known types of counter-torque control have certaindisadvantages. For example, it is at times extremely diflicult orimpossible for the operator of a counter-torque controller to determine,without trial, which direction the control handle of the master switchshould be moved to obtain a desired load movement since there is not auniform relation between the speed and direction of the load movementand the direction of the master switch movement.

For obtaining satisfactory control for long movements and shortmovements and inching operations it is necessary to combine single phasebraking with counter-torque control in a manner such that both cooperateto render the control system of universal application. In accordancewith this invention both single phase braking and counter-torque controlare so combined as to utilize the same secondary resistors, contactors,and speed control relays and therefore to simplify and centralize thecontrol for both of these opera- .operateat more than one value of motorIt is an object of this invention to provide a I which provides a simpleand ter-torque bra when controlled tlon.

\ power (not shown) ticns' as well as power lowering and power hoisting.

power plicatlons in the control of the secondary resistonce, but alsocomplicates the use of control relays which must be used not only toprevent too rapid commutation oi the secondary resistonce but ior othercontrol functions as well. The Y most satisfactory control relay .isresponsive to the, speed or a function of the speed of the hoistmotor.In accordance hoist motorare so connectedthat a minimum number is used,some of which are arranged to assessa- II I I a t V the terminal 9 isconnected to the conductor L3; I

For causing the motor III with invention .relays responsive to thesecondary frequency of the 1 speed. 1 I

control system'for' a wound rotor induction motor centralized control 01both counter-torquc control and single phase braking.

A "object is toprovide an' improved for an alternating current operatorcan select.

phase braking-torque. i

an important obiect otthls invention'is to so arrange the severalsections a range of highvaluesoi ing and a range 0! lower o! thesecondary resistance or a wound irotor induction motor that torqueuseful for hoistvalues oi torque useful:

for retarding overhaulingloads are available; .;A, correlative object isto combinewlthgthe ranges oi torque values.

I braking torque.

singlephase brakin A further object a suitablevalue-oi single I Afurther object lato provide a simple lnduction motor control systemwhichfis capabl loi I -'1 connecting the'motor selectively forpowerhoista I. log, power lowering, counter-torque lowering, and

is to provide an improved and I automatic means to discontinue thesingle phase I,

' connections when themotor approaches standzstill. Y

' Other objects. advantages m parent from the. following specificationwherein -i reference is mad to the drawings, in'whichr Fis. i .is acomplete power circuit'and agape; tial control circuit-diagram oi aicont yins the invention; I

Fig. 2 is-a diagrampf Fig, 3 is a graph torque characteristics or aninduction motor in accordance with" this inven- Y the remainder of thecontrol circuit of Fig. -1 and combines therewithto complete the circuitdiagr and v I illustrating certain'speed scribed can be used with adelta connected motor as well. The primary winding H has three terminals,1, 8 and 9. For causlngthe motor ill to rotate in a direction to lowera load the tenminal 8 is connected to the conductor Li through contactsHe, the terminal 1 conductor L2 through contacts 35b and ita, and

is connected to the connected through slip rings to a work comprisingalt-connected resistor 2ll hav 1 ing each of its .threebranches- 2i,

vdivided into five sections a, are referred to by subscripts to thereference 1 character of the corresponding branch. branch 2i comprisessections 2la,-2ib, 2lc,'2id, and 2H. The resistance sections Mr, 221',and 231 are arranged to be short circuited by 0011: a j tacts 25a, 1system for counter-torque control-for a wound I .rotor induction'motoLLZc Another'obiectis provide a controlsystem I motor in which eithersingle-phase or couna I and V in which the counter-=- torque iscomparable iii-magnitude to the single 'ancef sections sic, ohmicvalue-and I edited bycontacts.

- are arranged to ice -sired.. Preferably-the resistance of em, 2212,and 13a is about one-half oi the resistance of theresistornetworklo.

" scram one of the through contacts $817. to rotate .ln a direction tohoist a load the conthrough av conductor.

The motor idhas'its secondary b, c, d, and 1- which 25b, and zoo,respectively. The resist; nt -and 23a are of equal resistance sections;

280, ZZc and 23c together with the, section 22r are arranged to be shortcircuited by contacts 28;; and 28b; andthe additional resistancesections 2111, Mil-and 23d are of equal ohmic value and are arranged tobe short circuited by contacts 294; and 29b; The re-"' sistance-sectionsMr, 221 and 231 preferably aremay beunequalii dethe sections o a oiequal hmicvai'ue. but

.Acceleration,andspeedcontrcl relays SL M V 1 Bl are adjustablyoonnecte'd'm individual relay circuitssil, l8 50, respectively, which j"are connected across-voltage dividers 32, 42 and 52, respectively. 'Ihevoltage dividers" and 52 are connected in parallel through contact'siidbranches of the secondary r'e-.

sistorzo shown as the-branch 23,-one connection being adjustable alongthe section 2.3:: as shown,

and the voltage divider 32 is connected through [contacts rte across adifljerentbranch oi the resistor 29, shownias branch 2!, oue---connection being adjustable along the section 2 [a N as shown. The relay3! has 1 3M and normally closedcontacts 30a and-lib "and the relay 4!has an operating windingM'w [and normally closed contacts Ma and lib;"The.

relay iiphasian operating winding 5810 and normally closed contacts 53 i4 In the'relaycircuit 30 the relay'operating wind- I I Iiim-acondenserdland normally open conto Fig, 1-, a woundrotor induction;1 motor iflhas its tacts We are connected in series across an ad-.iustable portion of the voltage divider 32 to form a series'resonantcircuit 3911., Also connected in series with the winding @lw across anadjustable In the relay circuit dB the relay operating winding dlw, acondenser 43, and normally open contacts 65a are connected in seriesacross an winding polyphase net-' 22, and 23 are arranged to be shortcir- 26c andltbi the additional 25b, 22b and 232) are ofequal ohmicvalueand togethergwith the section Zir I I short circuitcdby contacts .Zla.and 21b; the-additionalreslstance sections are of equal ohmic value andi an operating winding adjustable portion the voltage divider form aseriesresonant circuit a. Also con- 1 nected in series with the windingllw across an adjustable portion oi the voltage divider 42 and formingwith the winding w a series parallel.

f resonant circuit 40b are normally open contacts I ing Slw and acondenser 53 are connected in 26d and nc'irmally closed contacts lib anda parallel circuitincluding a-condenser ll anda I non-saturablereactor-ll.

In the relay circuit ll the relay operating windgization of a relay 38having an operating winding 38w, normally closed contacts 88a and 880,

and normally open contacts Nb and 38d.

A multi-position master switch" having a plurality of circuit' terminalsll movable through three successive lowering positions and fivesuccesslve hoisting positions is provided m: controlseries across anadjustable portion of the voltage 1 divider 82, to form a seriesresonant circuit-Y For preventing excessive during coun ter-torquelowering a series resonant relay circuit his provided. The relay circuitInis connected. through an adiustable portion of the voltage divider 52.and comprises a series circuit including normally open-contactsttd, acon- ;lenser I23, and an. operating winding "he or a relay I havingnormally'open contacts 12m.

ling the operation oi the various contactors and relays which afiectoperation of the motor It. The master N has lowering contact segmerits82-80 inclusive, hoistina contact segments -1! inclusive, a contactsegment I. which ensages one oi the circuit terminals I inall positions,and a contact segment 71- which engages two 01 the circuit terminals BIonly in'the oil position. The contact segments 82-16 inclusive areelectrically interconnected. The pushbutton 31 is preferably mounted inthe operating The relay circuits II and I and the series tions 30b and40b 01 the relay circuits 30 and 40 are or the type disclosed andclalmed'in Patent f "resonant portions 30a and "a of the relay cir- 1cults l0 and '40 are of the type disclosed and claimed in Patent No.-2,165,491, issued July 11,

1939. to J. D. Leitch, and the series parallel por- No. 2,232,257,issued to A. H. Myles on February 18, 1941. As more fully described inthese patcuts, the electrical constants oi the capacitances s andinductances in the relay circuits ll, 80 and ii are so chosen inrelation to each other and to the magnitude and Irequency or thesecondary vvoltage drop to which'the relay circuits 30, M

l and 50 are subjected that the relay windings 3|w,' llw, and Slw'aresufliciently energizedat certain predetermined speeds oi the motor in tomaintain their respective associated contacts open,

v but are notsufiiciently energized at certain other speeds of the motorIn to maintain their respective associated: contacts open. Thereactances oi the winding Him and the condenser 123 are so chosen thatfor all safe countebtorque lowering speeds the contacts iZla remainopen, but

'1 are closed as 'soonas the counter-torque lowering speed reaches anexcessive value.

handle of the master switch II in a well known manner. r Operation Amore complete understandina of this invention may be had from aconsideration of its operation. Assuming that the switch is is closed,it the master switch I is in the oi! position, an

energizing circuit for the operating winding 36w taets 380 whichcomplete a circuit directly from The control circuits of Fig. 2 areenergized from I the conductors L2 and L3 through the conductors l3 andI4 when a knife switch I! shown in Fig. 1

is closed. A spring applied, electromagnetically released friction brake47 for the motor Ill has a direct current operating winding 41wconnected through normally open contacts 48a to the direct currentterminals of a suitable rectifier 49 having its alternating currentterminals connected across the conductors I I and H through normallyopen contacts 48b.

Operating means for all oithe contacts shown in Fig. 1 except those ofthe relays ll, H, SI, and

III are shown in Fig. 2.- The contacts shown in Fig. 1 and referred toby numerals with distinguishing subscripts, except those of the relays31, H, SI, and 12!, are parts oi the electromagnetic contactors orrelays shown completely m Fig. 2. Each of the complete contactors orrelays is referred to by the same reference numeral as its parts butwithout any subscript. Each oi the contactors or relays has an operatingwinding which is referred to by the reference numeral of its associatedcontactor or relay and the subscript w.

Referring now to Fig. 2, a low voltage protection relay 36 has anoperating winding 3610 and normally open contacts No. A push button 37the conductor Lt through the conductors It and 86 to the conductor 81 tomaintain the winding 38w energized regardless of the position of themaster switch 60. A. conductor 88 electrically connects the conductor 81to the circuit terminal 6| which is in engagement with the contact seg--ment I6 to maintain a connection between the contact segments 82-16,inclusive, and the conductor L! at all times when the contacts 36a andthe switch it are closed or when the master switch is in the of!position and the switch i3 is closed.

- Concurrently with the energization of the winding 36w, the operatingwinding 2510 is energized causing the contactor 25 to close its contacts25a, 25b and 25c which short circuit the resistance sections Mr, 222',and 231", respectively, and to close its contacts 25d and 252 whichconnect the voltage dividers 32, I2, and 52 across portions of thesecondary resistance 20. The winding 2520 is connected in parallel withthe winding 36w between the contacts 38d and the conductor ll. Thecontacts 38a are closed at all times to maintain the contactor 25 in itsenergized position except when the push button 3? is operated to itsclosed position described hereinafter.

In all master switch positions except the oil I position the brakeoperating winding "w is energized through the contacts "a and 48b andthe brake 4] is released. The energizing circuit for.

the winding 4810 which when energized maintains the contacts 48:; and652) closed is completed in all lowering positions from the segment 59and in all hoisting positions from the segment '55 through a conductor18 and the winding 481cm the conductor i controls, over a circuit to bedescribed, the ener- {conductor i l.

' Hoisting-- Assuming that a load is to be hoisted by the motor iii, themaster switch tfl may be moved to the first hoisting position to therebycomplete an energizing circuit for the winding ilw from the contactsegment ll through conductors 96 and 97,- the winding l'lw, a conductor98, and the normaily closed i terlock contacts led to the conductor is.In response to the energization of itsoperating winding ilw thecontactor ll closes its contactsila, I'll), and lie. Closure of thecontacts ill) connects the terminal 9 of the primary winding ii to theconductor L2, closure of the contacts ilc partially completes a circuitfromthe terminal I of the winding ll to the conductor L3, and closure ofthe contacts i'lc completes an energizing circuit for the winding 520from the segment ii through the conductor 95, the contacts He, thewinding i520, conductors 99 and 9%, and the interlock contacts ltd tothe conductor i5.

In response to the energization of its operating winding low, thecontactor it operates to close its contacts i541, iiib, ic, and I58 andto open its contacts Mid and I5). .Closure of the contacts i511 connectsthe terminal 8 of the pri-. mary winding ii to the conductor Li, andclosure ofjthe contacts i512 completes the connection' ofthe terminal Ito the conductor L3. Closure of the'contacts i5c'cornpletes the seriesresonant relay circuit 38c. Opening of the contacts led insures that theseries-parallel relay circuit 382) is interrupted during hoisting andthe contacts i5fopen an interlock with the winding flew. Closure of thecontacts i5e completes an energizing circuit for the operatingwinding66w of the relay is from the segment H through the conductor as, thecontacts ilc, a conductor t9, the contacts its, and the winding 46 10 tothe As a result of theenergization of its operating winding flew, therelay closes its contacts 66a to complete the series resonant circuitMia, opens its contacts 461) to. insure that the series-parallelresonant circuit fiillb is interrupted during hoisting, and closes itscontacts 1360 to'partially complete an energizing circuit for theoperating winding 27111 of the contactor 2'8. Y

When the master switch so is in the first hoisting position, thecontactors i5 and iii are in their energized positions and the motor idisso connected to the source as to tend to accelerate a load upward. Allof the sections of the resistance 29 except the 1 sections are connectedin the secondary circuit so that the torque of the motor 59 iscomparatively low, the speed-torque characteristic being shown by thecurve lfil of Fig. 3. As soon as the primary winding H is connected tothe three phases of the source, the

induced current in the secondary winding i2 is oi a comparatively highmagnitude and frequency so that the voltage drop across the branches 2iand oi the secondary resistance it causes energiriation of the windingsiiiw, the, and him of the relays 3!, ii, and hi. The relays 3i, ii, and55 are therefore in their energized positions and the contacts 36a, Bib,ilo, ilb, and

t a are open.

Movement of the master switch 60 to the secand hoisting position causesenergization of the winding 2511) over a circuit extending from thecontact segment 32 through a conductor 953, the normally closedinterlock contacts iiie, and the winding 2610 to the conductor it. As aresult assign V n V of the energization of its operating winding 26w,

ciently to permit v reclose. Closure of the contacts 3111 has no operthecontactor it closes its contacts 26a and 26b to short circuit theresistance sections 2m, 22c,

vand 23a. closes its contacts :260 in the series- By short circuitingthe resistance sectionsfld,

22a, and 2311, the operation of the contactor 26 to its energizedposition increases the hoisting torque, and the speed-torquecharacteristic of the motor i0 is now shown by the curve I02 of Fi 3.

As soon as the contactors i5 and i1 operate to their energizedpositions, the winding Size is energized. by the secondary voltage dueto theserics resonant nature of its energizing circuit- 3| to open itscontacts 3la the secondary and causes the relay and 3%. When thefreuuency of voltage decreases to approximately 0% of the synchronousspeed of the motor it, the impedance of the series res onant circuit 39ohas so increased that the energization of the winding 3lw has decreasedsumthe contacts Sic and 34b to ative effect at this time.

If the master switch is now moved to' the third hoisting position, or itit is already in that position, an energizing circuit for the winding21w is completed from the segment-i0 through a conductor H2. thenowclosed contact 3 lb and 480, and the winding 21w to the conductor [4.

As a result'o! the energization of its operating winding 271w, Zia and21b to short circuit the additional resistance sections 2th, 2%, and 23band closes its contacts 21c to partially complete an energizing circuitfor the winding 28w of the contactor 28. Short circuiting of theresistance sections 21b, 22b, and 23b causes the torque of the motor illto increase again and the speed-torque characteristic of the motor iiiis now shown by the curve hosting position, or if it is already inthefourth position, an'energizing circuit for the winding 28w is completedfrom the contact segment 13,

through a conductor 9i, the now closed contacts- Zlc and mo, and thewinding 23w to the conductor i l. As a result of the energization of itsoperating winding 2810, the contactor 28 closes its contacts 280, and28b to short circuit the addi' tional resistance sections Zic, 22c and230 and closes its contacts 230 to partially complete an energizingcircuit for the winding 29w. The torque of the motor I6 is againincreased and the motor it now operates along the curve 104.

When the motor it] reaches a speed of approximately of synchronousspeed, its secondary voltage and frequency are such as to cause adecrease in the energization of the winding 51w a value corresponding tothe contactor 21 closes its contacts of its synchronous speed theenergization of the relay M as a result of an in- "hi8hranga',,

Returning the master switch Oil to the oi! position causes step by stepinsertionof the resistance sectioned, c, b, and sin theorder named, and

' I interlock contacts I! the master switch BI is now moved to the canhoisting position, or u it is already in that position, an energizingcircuit for the winding 2820 mg winding zaw, the contactor 2o closes itscontacts 28a and 29b to short circuit the additional resistance sections2ld, 22d, and Md. The torque now operates along the curve M5. All of thesecondary resistance 24 is now short circuited and 1 is completed ,iromthe contact segment 14 through 2,886,464 u 5 of the relay H whichpermits the contacts it; tactor 26 and the contactors I! and i1,respecto reclose. tively.

The contactor 28 operates in response to the predetermined amount of theresistance 20. The

operation of the contactor 28 to its energized position also causesclosure of the contacts 260 and 26d in the relay circuits and '40,respectively, completing the series-parallel resonant oi the motor I0 isagain increased and the motor the motor accelerates to its normalrunning speed, its actual speed depending upon the size oi the loadbeing hoisted. Inasmuch as the push 1 button 31 has not been closedduring hoisting operations, the resistance sections Zlr, 221-, and Iirhave been short circuited, and the resistor 2| has therefore beenbalanced overall steps 01- eral hoisting torque values throughout arelativel acceleration, and the motor 14 hasprovided sevconsequent slowdown and stoppa e of the motor ,m. At the-of! position, the winding 48wofthe relay It is deenergized and the contacts at and ubopen to causedeenergization or the brake winding 41w and consequent application'oithe brake 4'! which assists in bringing the load to a standstill andholds it in its heated positi0n.

Ii'the master switch it is moved operating windings liw; llw. and'flware enercircuits 80b and b, respectively. The conditions of operation ofthe relays 3i and -4| are of nov consequenceiwhile the master switch isin the first lowering position and the eii'ect of the series parallelconnection is described in detail hereinafter in connection with thereturn of the master switch ill to the oil point.

A portion of the primary winding ll is'now short circuited and a portionis energized by a single phase current from the source through theconductors L2 and L3. with the resistance sections b, c, and d now inthe secondary circuit, the braking torque of the motor I0 is shown by thcurve I" oi Fig. 3. This type of braking connection is claimed and morefully described in my Patent No. 2,233,501, issued March 4.1941.

While the single phase braking connections 'are made, no downward motortorque is produced so 7 that small loads are not forced downward, but itoverhauling load is on the hoist, the motor V irom the ofl' position tothe first lowering position, the brakeexerts a braking torque whichvaries as shown by the. curve I06. The braking torque increases inmagnitude as the speed increases even at 5 speeds above synchronism.

A small amount of downward motor torque is obtained upon movement of themaster switch I to the second lowering position; The windgized insuccession in the ordernamed. The ener-- gizing circuit for the windinglira istrom the contact segment 52 through a conductor 9! and thewinding lBw to the conductor l4, Theenersizing circuitior the-winding "wis from the contact segment 65 through a conductor 84, the now closedinterlock contacts ltd, the normally-closed interlock contacts l5), andthe winding i810 to the a conductor l4. The energizing circuit for thewinding 2810 is from the contact segment I through the conductor 94, thenow closed interlock contacts ltd, a conductor 85, the now closed 18c,and the winding 28w to the conductor l4.

The-contactors l8 and ll operatein response} to the energization oftheir operating windings l6w and law to closetheir contacts lia, "b,ila',

' and lab which connect the primary winding ll I for single phasebraking. The terminals 1 and.

8 of the primary winding H are interconnected by the contacts Isa-and18b and a point on the interconnection is connected to the sourcethrough the conductor 39, the contacts'lia, and the conductor L2. Theterminal 9 of the primary 7 winding II is connec'ted'to the sourcethrough the contacts lib and the conductor L3. Operationoi' thecontactor. it to its energized position also closes the contacts. Mewhich complete a holding circuit for the winding liw which becomeseffective when the master switch 80 is returned to the ofi position ashereinafter described. Operation of the contactor l8 to its energizedposition also opens the contacts use and lBd which serve as interlockswith the conings. ltw and "were deenergized upon movement of themaster'switch 80 to the second loweringposition by interruption oi thecircuit between the contact segment 85 and the conductor I4 and thecontactors l8 ard 28 return to their F deenergized positions.Deenergization oi the winding 2lw'causes the contactor 26 to open itscontacts 262: and 26b to remove the short circuit from the resistancesections Ila, 22a, and 23a. The winding liw is maintained energized andthe windings ltw and 48w are energized to .cause operation of thecontactor l5 and the relay 4, respectively. The energizing circuit forthe winding I510 is from the segment 84 through the conductors H3, 80and 98, the winding liw, the

conductors and 98, and the now-closed interlock contacts lid to theconductor l4. The energizing circuit for the winding 48w is from theconductor H3 through the now closed inter ock contacts; lie and thewinding 46m to the conductor l4.- Deenergization of the winding lliwcauses the contacts in and lib to open, thus interrupting theinter-connection between the terminals 1 and 8. Energizationc! thewinding "to causes the contactor I! to close its con-.

tacts ida and lib so that the primary winding H is now connected to thesource through the contacts Ila-and the conductor Ll, the contacts llband Ito and the conductor L2, and

the contacts l 61; and the conductor L3 thus causing a downward motortorque to be exerted, its magnitude being shown by the curve llll.

'I'heccntacts 28c and 28d also open in the second lowering position tointerrupt the series parallel resonant circuits 3% and 40b,respectively. Operation of the contactor l! to its enof thevoltageacross the cycles per second if a. 60 cycle source is 'As themotorapproaches zero speed, both the 1 the relays 3| and 4i 28a and 261)which the holding, brake 41 from zero cycles per second at synchronousspeed in one direction of rotation to 60 cycles per second at standstilland to 120 cycles per second at synchronous speed in the oppositedirection of rotation. The other current is a negative sequence currentthat varies from 120 cycles per second at synchronous speed in thedirection causing the positive sequence current to be at zero frequencyto 60 cycles per second at standstill and to zero, cycles per second atsynchronous speed in the opposite direction of rotatiomthat is, atsynchronous speeds, one of the two sequence currents has-a frequency of120 cycles per second, whereas the other one has a frequency of zerocycles per second and at zero speed the frequency of the currents isequal and is 60 cycles per second. Y

The series parallel resonant circuits 30b and b are set to causeoperative energizatlon ofv the windings Ilw and llw when the frequencyvoltage dividers 12 and 42 approaches the frequency of the source, or 60assumed.

positive sequence currents and the negative sein excess of one-half ofthe normal value al-- though the other at the same time have a currentvalue of nearly zero. '35? using both relay circuits 30b and 40bduringsingle phase braking and connecting the contacts Sla and]!!! in serieswith the winding liw, it is always possible to have a suillcient voltagedrop across either branch 11 or 23 for one or the other of the windingsH and w to be en-f v ergized to effect operation of the contactor I 6 toiits'deenergized posltio quence current are approaching 60 cyclesperduring single phase braking as long as the motor i0 is rotating abovemum speed. The frequency-current curves of the series-parallel resonantcircuits b and at all frequencies substantially above b are peaked at 60cycles and are at a low current value and besecond, and therefore bothcurrents affect the Y relay circuits 30b and 40b in a similar manner.The windings llw and w remain ,deenergized f and the winding 3820 to30'- a predetermined mini low 60 cycles per second. As the motor I0 isretarded due to single windings 31w and to increases rapidly at apredetermined value of motor speed close to'zero speed and causesoperation of either .or both of The contacts 3 la or 4 la, or both,thereupon open to interrupt the circuit to the operating winding Iiw ofthe contactor l6. Deenergization of the- IS to open its; circuits to'thewinding lfiw causes the contactor contacts 16d which interrupts theresistance 20. The relay windingsflmflmand Slw consequently remaindeenergized" durin counter-torque operation. The relay 8| also phasebraking torque,'- the current through one or the other or both of the 1to their energized positions.

windings i820 and 26w and the contactors "and 28 thereupon open theircontacts I81: and Nb and the contacts Ila phase braking connections. Themotor II is now rotating at a slow enough speed to permit to bring it tostandstill. When the master switch BI is moved to the of! position fromthe lowering positions, both single to together withthe opening of andNb removes. the single phase braking and friction braking are in effectsince the relay 8 is deenerglzed and the contacts 48a and 48b are opento cause deenerglzation of the operating winding "w of the brake 41 assoon as the off position is reached. The motor I0 is thus quicklybrought to a standstill and the single phase connections automaticallyremoved to prevent a continuous flow of current through the shortcircuited portion 01 the primary winding.

It is to be noted that the relay circuit 30 is, connected for,energization from the branch 2! of the secondary resistor 20 whereas therelay circuit 40 is connected for energization from the branch 23. Thisis because at or near standstill, when the operation of the relaysil and4| is to be eilfected,the secondary current is unevenly distributedamong the three branches of the secondary circuit. In one position orthe secondary permits the contacts 360 of V v and interrupt the circuitthrough-the conductor 81 from the conductor It to the conductor ll.

n it is desired to'lower a load by countertorque control, the pushbutton 31 may be closed and the masterswitch Gil moved to any one of thehoisting positions toeomplete a circuit from the contact segment 1! 98and 91, a conductor i through the conductors H, the push button 11,

relay-38 in response to the energization of its operating winding 38wopens-its contacts "a in the conductor, 81 to deenergize the windings25w and' 3810 and closes its contacts 38b to complete a circuit from theconductor II to the conductor 88., Deenergization or the winding 38w therelay 38 to open Deenergization oi the winding 25w permits the contactor25 to open its lie to interrupt the nect the voltage dividers 32, I2,and 52 from the opens its contacts 38cto interrupt the circuit to I thewinding 2910 thus preventing closure or the.

contactor 29 during counter-torque operation,

and closes'its contacts 38:! toirender the series resonant relay circuitIneffective.

, If the master switch 60 is in any or the hoist-v ing positions and thepush button 31 is closed, en-

ergizing circuits are also completed from the v contact segment H- tothe conductor H through the windings llw, Iiw, and 48w causing operationof the contactors l5 and i1 and the relay 46 in the same manner asdescribed for hoisting operations and the motor it exerts a hoistinstorque. I

Ii the ma sterswitch 60 is in the first hoisting position, all of theresistance 20 including the r Y sections is effective and the torque ofthe motor I0 is now extremely low and the speed-torque master switchcharacteristic is shown by the curve 101. the portions of thespeed-torque curves to the left of the zero point of the speed axis areshown for counter-torque operation, since countertorque control is onlyused when the load is driving the motor ID in a direction opposite tothe rotation of its magnetic field.

If an increased counter-torque is desired, the 60 may be moved to thesecond Only oi the branches 2| or :3 might the conductor H. The

contacts 25a, 28b, and}. short circuit connections aroundthe resistancesections Ilr, 221', and 231' and to open its contacts 25d and etcdiscon-q Fascists position in the ionic direction." in this pen-,1toriiue'operstion'due to the fact that the relsy tion on energizingcircuit tor the winding 2620 is circuits 89,, and 50 are deenergizedbecause the completed from the oontoct segment 12 through contacts 225dsnciztc are open.'-

I the conductor 80, the interlock contacts E2, and If the lowering speedshould become excessive the windingzow to the conductor M Theconwhilethe mnster switch 60 is in the first, second; tactor 26 closesin'response tothe energizistiom or third. countehtorguepmitions,thecontsctor of itswinciing 2620 to close its contectsZQuenci' '28 iautomatically operated to its energized posi- 26b which short circuitresistance-sections tic tion. with the contacts 280; and-zw'closed the220,, and 23g; since-the'ce. sections- 2i1, "speed torquecharacteristics is given by the curve r 221-, and 23:- srestill in thesecondarycircuit, no as inthe fourth position thus tending'to thesecondary roe 26 is still balanced; greatly reduce the loweringspced.i,='

I and its ohinicivalueis such as to cause the I Automatic operation orthe-cunts; or 28'duriii to have a speed'torque chorsctcristio. cs shown,ing coimtentorque lowering is eflected by. the

by the curve ill.

'. relay circuit I20. As the lowering speed ciuring- Movement of the..15 counter-torque operation increases the frequency hoisting positionyi'th the push button?! closed or the secondary currents of the motoriii also;

i causesan increase in the'coimter-toru e frontier increases;At'synchronous speed it-is twicethe the curve [98 to the curvei, In thethird D081 frequency of the source; The series resonant cir 'tionthe-contactor 21 is operated to its energized- 1 cuit I ZG maybeadiustedso as to causeincreased position due to the 'energization of itsenergizstion oithe winding lZlw at any suitable aim over thesame circuitdescribed, in 'ccnn'ec-' high treqllencm'foi' example twicelinefrequency.

' tion 'withthe hoisting operation. The closure of Energizction oi'thewindingfliw causes closure I the contacts ila-anci ib csuses'shortcircuiting oi; the contacts Him-which complete; a circuit of theresistance sections 2 lb 226,, 2 in. and 28b. from the energizedconductor. 88 th 'q h. the con-- The'resistoflfl ishow'unhalsrihdshoethe re j 1ductor libntothc winding 282m The contactor II sistorzir-hes'been removed. iromf the branch at tf 23 thereupon" operetes toincrease the comic:-

and the" sections ,2 2r anti 231; are still eiiective j torque to'it's11 .1 thus slowing down.

- in the branches Hand 23,'irespective1y; "the load- II I t 4 Ybalancing results in. a e ifea o in th .5 It is coh rent that the'seccndaryresistence 20 r v rse or ho insmmu goi' bs mo in from aso-constituted that era-nee'onhigh torque lthat'which would occurii theresistance-2o were values useful 'i'o'r hoisting and a range of lowbalanced. This decresiseiiveiue oft-reverse torque torque .vslues usefuliorretarding overhauling is-shown b? the speed-torque characteristic;m9; loads ere made-freadily. available by simple ma- If the resistancesections Brand 23: were short. gnipulations of the push buttonjl and themusterv *circuitd as during hoisting operations, the'speed switch BILFurthermore, this simple; and cen-' torque: characteristic wouldhecurve-ifl; 1t=isv *tralize controi'elso provides for single phasejdition oi the" secondary resistance 20 e? grestiyre ment of anoverhauling 1osd. ;"'j

.thusseenthatiby pro an imbalancedcon-v9 1." braking.

the push button it closed. In the P II source sbthat the winding law isdeenergizeii li n th vwmw fvn is ontretedto l fi mousing'opening oi thecontacts 48a and 48b and p s i n d o n s t n 011% Winding consequentdeenergization' oi the brake winding aewovertm e circuit descinconnection em 4 with the ho operation. Operation of the-' 9 "in a-53 mgto x hoistmg contoctorfifi to its one! position causes cio-- j t g m thupper rang afterjcperationin 'sure of the contacts lac-and 28hwhichshort cir= I wits t s c n 2210! 2211.93? i. open the push button 31and movethc master 7 'Hbe nsvst i nom s Since-it 'isnot no ordesirabietoihave I I I I I I Opening'ofthe push button'sl at anytimel'riuceclhoistingtoroueis obtained whl s m nduring counter-torqueoperationre'sults inim oily insuiiicientior' hoistins a load; butWhichho mediate stopping of the motor it. This isbe; is; sumcient for.retarding the downwardnove- 'cause opening of the push button 31interrupts I I I I i=4; the energizing circuit to the winding arc-whichA further i increase 0!" I unter toruue; is lob-g2 f ceuses therelay 38to open its contacts 38b and f I tsined upon movement of themssterswitchto' close; it contacts 1am. Opening-oi the contacts ,to the iourthhoistin position while maintaining; 38b disconnects the master switchBil from the theeounter-torquopositions, it is necessary to'Thaw-Omitfihflracmisficbfthemwl switch back-to the of! point so that acircuit to wh by the -iii t 8isn3QJ5 'the 36:0 and zsw can bereestablished *th'rough'the contact segment-i1 and the contacts Ieigreiiter'v clue oi counter torqueisvailsbie than .iuaimk ingCOilhtQf-GQMMQ in $11.5: 2 I to chsngein the "tor t'is I I t 'mgt u is wrin I branches each having a terminal adapted to be "contacts so: Iinterrupt thefcircuit Gimmes! is eieminfil of s on wind- I that obtainedin the mural: position. movement;

i h. til it 21-60; o the master mm to gfi g i gy; QI rotor inductionmotor control system which come fore movement'oi master switchWYtothe fI fifth hoistine' on'while-ltho can: button 8!- isclosed---not causeoperction'oi the tector some the torque characteristic the motor i9 rem'raJity 'of resistance sections connected in'series position, Y I eachgroup comprising one or more sections of The waters 2?, 28,-Q 29 arinterlo k d g eachbranch, of additions! short circuiting means thsttheyno It|u.. i m opemtein due operstiyely associated. with at least some ofthe to the interlock comets his one see. The consections of more thenone of t srcmps, resp tscts 39h, 69h, nnfi his ore i, cote.- tively, endeaohoi' said additional short circuit- 1. The'cornbinstion our; steepess witiij prises aresistance network having' a. plurality-of closedpolyphsse. network with said secondary- ,windinm-esch-oi said branchesincluding a plu- I with. other; and means operable towshort M-mjocircuit groups of resistance sections in sequence,

ving means being'operable to render its associated g of said motor andconcurrently to connect a,

group balanced and unbalanced selectively. portion oi the primarywinding to a source of 2,. A control system for a polyphase woundrosingle phase power, whereby, upon operation of tor induction motor,comprisingaresistance net-v said switching means, the primary windingworkhaving a pluralityof branches each having said motor is connectedfor single phase braking,

a terminal adapted to be connected to a terminal and in that said shortcircuiting means is 01;)- o! the secondary'winding-of. said motor to01m, erable, while the primary winding .is connected when so connected,a closed p lyphase network tor-single phase braking, to short circuit aDre;

with .said secondary .winding; each 01 said; r,.determined--numberotsaid resistance groups branches-comprising .aplurality of conductingi w dncontrol system in accordance with claimsections connected inseries with each other, shortt 4 characterized inthat said system includes i;

- circuiting means-operable to short circuit in 81101;" switching meansoperable to short circuit a por-'- I cession groups ,ofconductingsections. eaz'ihcff tion-ofthe primary winding of saidmotor and s whichgroups-consists ot-at least one sectirmot concurrently to connectaportionof the primary each branch, at least onelsectionin each of somewinding to a sourceof singlephase power, whereof the groups havinganunequal ohmic resistance by, upon operation of said switching means,the

value withrespect to at least one of 'theother primary winding of saidmotor is connected for sections in the same group, and means for altersingle phasehraking, said short-circuitlng means 9 in! the resistance ofsome of the sections'to cause being operable,- while he primary windingis" all of the actions in any one of'thellast inan 1 connected iorsinglephase-braking, to.short-.cir- "-tioned groups to have the sameohmic-"value as cuit a predetermined portion of each ofsaid-re ;v I Jthe other-sections in the same group s stance branches; a v

3. A'control sys em-for apolypha'sewoundLn;..'"p1 7; A-motor 'controlsystem for hoists and the tor inductionmotor,comprisingaresistancenetjlikevsuhject to overhauling descendingloads,

' work having a plurality of branches each having =2 comprising apolyphase wound rotor induction a terminal adapted tobeconnected to.aterminall I motor for driving the hoist, means for control- 01 thesecondary winding-or'said inotorto 1orm',-.,;' ling the direction ot'andspeed of said motor 1 J i when so connected, aclosed opolyphase networkcomprising-a plurality ofcontactors and a multiwith saidsecondaryfwinding, each-ot,; :said. fi position manualreversing controller forcontrolbranches ccmprising'aplurality of resistance sec-' 5 ling saidcontactors, saidcontroller having an .vtions connected-in serieswitheachothenmeans, ofi'position and a plurality of hoisting positions,

, operable to shortfcircuit groups-oi resistance'sec-j I tions insuccession, each or said groups consisting of at leat onei section 01'each branch. each. 01-. 1

' nal oi its respective branchiby an equal numberf 'spect to othersectionsin the same groupfand 7 sections to cause all of the sections inany group;

.:a normally balanced resistance network con-F r nested ina closednetwork with the secondary winding of said motor; additional resistanceole-" the sectionsinone oi'saidgroups being c'onnectedgg meritsconnected, in at least one branchof said 1 directly to the said terminalor its respective, ,network, a contactor means operable when enbranch;each of the sections in each of the re, v ergized for short circuitingsaid additional resisto maining groups beingseparatedrirom the termiance elements and operable when deenergized to t remove said shortcircuit, a contact segment on said controlleriorpartially establishing acon-'-- troljcircuit tor-said contactor means while said v 7 controllerisln "said; hoistingpositions; and a r means for altering the resistanceofsome of the f manual meansfor. completing said partially c0 m-, gpletd circuit tdcausedeenergizationot said con-- tohave the sameohmicvalue. 1 45.,tactorj-means, 4.111s combination including apolyphase 8. At mctoroontrol' 'aystemior hoistsyandthc of sections, someof the sections in some oisaicl groupgbelng of unequalohmdcvaluejwithrc- I wound rotor induction motor subject; tooverlikesubiect to'overhauling descending loads, comhauling loads andhaving a polyphase primary winding connected to a source of polyphasepower hase secondary windinga plurality of resistance network withthesecondarywindingjot said mo;

- terminal of said secondar winding and torming I ofsaid'niotorfcomprising a plurality oi electrowinding, each of saidbranches comprising a plu itroller, some of said; contactors being,adaptedshort circuiting means-operable to-short circuit said controllerhaving an oil-position; abraking l of the hoist, groups ofsaldconducting-gections 'tactfsegment'means on said controller operable eachor which consists of at leastonesection of -;fco when saidcontrollcrismovedto said braking po';

having equal ohmic-value, and means operableset npsinglejphase brakingconnectionsQasecond only while said motor isconnected-forhoisting'contact segment. means on said controller op operations to change theresistance "oi portions 1 erable. when someoithe controllerpis moved toof said conducting sections relative to other per the running positionstor, partially completinga prising a polyphase: wound rotor inductionmotor a I iordrivin fihe hoist, a secondary resistanceconnectedin;ainormally'balancedpolyphase closed for hoisting and loweringoperations andapoi y branches each having a terminal connected ton;tor,means fol-controlling the direction and speeda closed polyphasenetwork-with'said secondary """magnetic'contactorsan'd amanualreversing.con

rality of series connected} conducting sections, I. whenenergizedto'unbalancesaid closednetworh in steps, during hoisting andloweringoperations position and. aplurality of. running positions,c'orr-i' each branch, all of the sections of thejsame group sit'ionfol-energizing some;-oI saiicontactors to,

1 time to render said closed networlcunbalanced, circuit. forcausingoperation-of saidcontactom .1

whereby operation or said short circuiting means adapted to unbalancesaid. closed networlcfandv while [said resistance isichanged controlsthe for energizing some of said-contractors to connect holsting torqueof'said" motor to regulate the f the motor to a source-01'power'foriexerting a" lowering speeds of said overhauling loads. torqueopposed-to the torquexot the' overhauling 5; A control system inaccordance with claim; load, and manual means operable for complet 2characterized in that; said system includes ing said partially completedcircuit, whereby switching means operable, while all of the. sec-;when-said manual means is operatedwith the. tions in any group have thesame ohmic value, controller in some of said running positions some toshort circuit a portion of the primary winding or said contactorsoperate to unbalance said secondary resistance and the motor torque isvariable at will over a range above and below said braking torque.

9. A control system in accordance with claim 8 characterized in that acircuit control means is provided for rendering said manual meansinoperative to further control said contactor means until saidcontroller is returned to said off position.

10. The combination in a control system for a polyphase wound rotorinduction motor having a polyphase secondary circuit including aplurality of branches and having its primary winding adapted to beconnected single phase to a source of power, a control means operablefor controlling said motor, and a relay means connected to one of saidbranches and responsive to a predetermined electrical condition oi saidone of said branches while the primary winding is connected single phaseto said source of power for effecting operation of said control means,oi a second relay means concurrently connected to another of saidbranches and concurrently responsive to the predetermined electricalcondition of said other branch for effecting operation of said controlmeans. a

11. The combination with a polyphase wound rotor induction motor havinga predetermined amount of resistance included in its secondary circuitand having a portion of its primary winding' short-circuited and aportion of its primary winding connected to a single phase source ofconnected. v 12. A control system fora wound rotor induc-.

tion motor subject to overhauling loads and having a polyphase primarycircuit and a polyphase polyphase secondary vresistance network,switching means operable ior connecting a portion 01 the primary windingof said motor to a source of single phase power, for short-circuiting aportion of said primary winding, and for including a predeterminedbalanced portion of said secondary resistance network in the secondarycircult of said motor, whereby, upon operation of said switching means,said motor is connected for single phase braking and a braking torque isproduced which opposes the torque of said overhauling load, and meansoperable for connecting said primary winding to a source of polyphasepower to cause the'motor to exert a motor torque opposing the torque ofsaid overhauling load, of means operable upon operation of said lastnamed means for connecting an unbalanced portion oi said resistancenetwork in the secondary circuit, whereby the motor torque opposing thetorque of the overhauling load is caused to be comparable in magnitudeto said braking torque at some speeds of said motor. 7

14. In a control system for a polyphase wound rotor induction motorsubject to overhauling loads and having a primary winding and asecondary circuit which includes a secondary wind-' ing and a normallybalanced ach'ustable resistor, means operable to short circuit a portionof said primary winding and to connect a portion of said power, andextraneous means for driving the I secondary circuit comprising anadjustablere- 1 sistance adapted to be connected in the secondarycircuit, a master control element having several I positions ofmovement, an electricallyoperable 'iriction brake, means operable whensaid master control element isin one position to apply said j frictionbrake to hold said load at standstill,

means operable when said master control element is in another positionto release saidbraka to short circuit a portion of said primarytoconnect at least a portion of saidjprimary winding across asine-lephase source of power,

[and to associate saidadlustable resistance with the secondary winding,whereby single phase braking connections are oompletediand a brakingtorque isproduced upon rotation of said motor by ssid'overhauling load,and means operable,

when said master control element is returned to said one position, toapply said friction brake" 1 and-to prevent the removalof said singlephase braking connection, and said last named means comprising a pair051 relays each adapted to be 1 connected so as tobe responsive to apredetermined electrical condition of a different phase of the secondarycircuit.

13. The combination with a motor control system for hoists and the likesubject to overhauling descending loads, comprising a polyphase woundrotor induction motor for driving the hoist, a

1': end; closed through an adjustable resistor, means i -incoperations,means operable to short circuit a portion of the primary winding oi'saidmotor andto connect a portion of the primary winding 'to' a single phasesource of power for braking primary winding to a single phase source ofpower, means operable while said primary winding is so connected toinclude a predetermined balanced amount of said adjustable resistor insaid secondary circuit, whereby said motor eager-ts a. maximum singlephase braking torque opposing the torque at the overhauling load overa'speed range extending from over synchronous speeds tozero speed, meansoperable to connect said primary winding to a polyphase source of powerto cause said motor to exert a motor torque opposing the torque of theoverhauling load, means operable to vary said adjustable resistor insteps while said primary winding is connected to said polyphase sourceof power, whereby several values of counter-torque are available, andvsaid single phase braking torque at some speeds of said motor. 7 I v l15. A control system fora polyphase wound rotor induction motor havingits secondary ciroperable to connect the primary winding of saidmotorto' a source of polyphase power for motoroperationa-e plurality orrelay circuits which are eifective'to control motoring andv brakingoperations. each oi sold relay circuits including an operatingwindins,-a condenser. and a parallel 1 combination-including a parallelconnected con-=- 'denser and reactor, means connecting the windin'gandthe condenser oi one of said relay cir cults in series with eachother across one phase of said secondary circuit during motoringoperations. and means for connecting the operating winding and theparallel combination of at least two of the relay circuits in serieswith each other,

each of said relay circuits when connected as last described beingconnected across a difierent phase of said secondary circuit duringbraking operations.

16.1111. control system for hoistin: mechaforcontrollins thedirectionond magnitude or if the torque-of said motor. means responsiveto the controller at one station for connecting the stator o! the motorto a. polyphase source of power so that the motor exerts I. hoistingtorque tending".

to raise the d. 130mm -n responsive to the controller for warm saidrestitorv to vary. --said ,hoistin: torque throuahout: n nuximum range,means responsive to the oontroller etjan-..

oior'short-cirouitine 1o portionot;

responsive to the controller at still'mother e21 .uo 1oz connecting thestator to a poiyphue source oi. power aothat the. motor exerts: torquetending to force the load downwam'oi means associated with saidcontroller and operi able for causing said adjusting means to adjustsaid resistor when said stator 'is-conneotedto the p lyphase souroeotpower so that the motor exerts a torque tending to' raise the load,odjnst ment of said resistor by operation of said manual means causingsaid hoistinztorque to 1 1 the stator and connecting a. portion or thestator. "to a sinzle phase source or power, and means invariable, :oniythroua'hout a minimumranze.

